NGB air flow design help needed

[iriebowl]

Sup everyone I finally got the ok to build a NGB cab. I have the dimensions drawn up and will be 47"H x 48"W x 24"D flower cab47"H x 33"W 24"D moms/veg cab 30"H x 15"W x 24"D utility cab 18"H x 15"W x 24"D. I will be using a Stanley blower as my exhaust fan, but if I need to I'll get a actual blower like a vortex. Flower room will use two 150hps in a bake-a-round with 4" ducting. Mom/veg cab will be either 4-6 26w cfls or 4 18" 15w flouro tubes. I live in a fairly hot and humid area with temps ranging from 75 degrees F low to 95 degrees F high. My cab will be in my basement with hopes of it being easier to regulate temps. This will be my first attempt at a semi perpetual soil grow depending how things do in the long run.

Now that you have a basic idea of what I will be doing I need help figuring out how to get proper ventilation while keeping negative pressure in the cab. I read that the "passive intake should roughly be double the size of the exhaust" does that apply to NGB type cabs?? If "yes" my cooltube going to the Stanley blower is a 4" diameter(area of 12.6 squared inches) and I need to double that area for my passive intakes(flower to veg). I'm gonna need 25 square inches worth of intake then double up again making it 50 for the main passive intake. Now, to me that seems like too much intake area to use on this cab but I'm always wrong and this could be one of those times. If I use 2" PVC (3.14" area) or even 3" (7.1" area) I'm gonna need at least four 3 inch or eight 2 inch PVC to make 25 square inches worth. Then double up again for the main passive intake on the veg cab, a whopping 50 square inches. For that I plan on using a 5" x 10" vent like in TICK'S SOGG'N BOX if they come in that size. Can someone let me know if I'm doing this right? If not how did everyone else calculate intake/exhaust sizes for a NGB cab?

Gonna purchase the wood and mock it up til I have the ventilation finalized. On a side note I'm gonna use 1/2" plywood (not sure what grade til I see whats available) or should I bump up to 3/4". Framing will be enough to stay rigid but still have alot of grow space probably 1" x 2" something like Connoisseur300's NGB cab. Also from TICK'S SOGG'N BOX will be the base frame to place the cab on. Gonna need the ability to level it easily since my basement is not flat or level LOL. Now that I'm done explaining I hope I can get some answers to my ventilation questions so I can actually build it.

Heres a thankyou pic of my last grow

 

[DiscoDuck]

If you plan to use 3/4" plywood, you'll probably not need internal bracing unless it helps you assemble the pieces. I make a variety of plywood cabinets and the strength is higher than most any other material. If you plan to use internal bracing, it doesn't have to be big and bulky. One inch square bracing is more than strong enough for the cabinet and won't weigh a ton when you decide to move the thing. Some folks think the bulky designs are necessary but if you're good with the tools and assemble the pieces nice and square, even 3/8" plywood with 1" bracing will take a lickin' and keep on tickin' for a long time. The Stanley will probably work fine for your size box with regard to air flow. It will depend what kind of scrubber you use because these reduce air flow. It's always best to have a little too much fan than too little. A large fan that is slowed down with a speed controller may even be quieter than a smaller one on full speed.

Each individual chamber inside the grow box will need 2:1 intake vs exhaust. If you feel this is excessive, start with less intake, test the fan with the door closed. Does the fan rpm increase significantly? If so, you need more intake. If your grow box has dual chambers, you'll have to decide whether to use a single vs multiple intakes. Each have their advantages and disadvantages.

With a single intake, (not single hole but located in a single chamber) air is circulated through the entire box prior to exhaust. The advantage of this method is you don't have to "tune" multiple chamber intakes for optimum air flow. The disadvantages include the fact that each chamber will heat the air somewhat. By the time air is flowing into the last chamber prior to exhaust, it's hotter than if it went through only one chamber. If you go to the trouble of sealing and venting the light area from the grow area, this method works best.

If you decide to put intakes in multiple chambers, (the method I chose) you'll have to "tune" the intake size so that air flow is distributed according to the relative size and air flow needs of the respective chamber. In other words my cabinet is divided in half, veg and flower. Equal intakes in each chamber will result in equal air being exhausted from each chamber respectively. My flower chamber produces more heat than the veg chamber so I want a little more air flow to go through the flower chamber. Giving the flower chamber more intake (and reducing veg intake proportionately) will increase the airflow in the hotter area.

Another thing to consider is whether or not you plan to use some type of bug screen over the various holes you'll be cutting into your box. Window screen is the least restrictive and probably won't reduce air flow. Some folks use nylons, this stuff will fill up with dust and need cleaning now and then. I ended up using scotchbrite pads cut to the size of the intake holes. This stuff reduces air flow more than window screen and fills up with dust like nylons. I'm also using it because it blocks light that leaks through the intake holes. I'm having to clean or replace the scotchbrite twice a month. This is a major pain in the ass so I'll be designing a new light trap in the near future.

One other thing is important. While I know you're already aware that heat rises and cold sinks, intakes and exhausts should be located as far from each other as possible. I recommend putting your intakes in the floor of the cabinet, this is where your cab will draw the coolest air in the room it's sitting in. The cabinet exhaust will probably be located on the back panel of the cabinet so it's a good idea to make sure the hot air is deflected in a direction other than down to the cool air intake area. Although the difference in hot air and cool air is enough to keep them segregated under normal circumstances, your cabinet will create a loop of air movement great enough to suck in heat from above. I made a shroud for my exhaust that forces the exhaust air in a direction away from the intake.

Here's a shot of the bottom of my cab with the intake holes. The veg chamber has 6 1" holes and the flower has eight. This allows more of the air to flow through the flower chamber. My exhaust fan size is 4", the utility chamber has eight inches of intake split between the flower and veg chambers. This means the veg and flower chambers together need about 16" of intake to make it all work. I was a little scared of drilling too many intake holes so I drilled 14 holes and tested the fan with the doors closed. The rpm increases only slightly, letting me know I'm pulling negative air in the cabinet like I want. If the fan speeds up noticeably during the test, I'll try drilling one more 1" hole. Test again, etc.


Lastly, if your floor isn't level, a cabinet base with 4 feet will not teeter as bad as a box style base. This will assist air flow into the bottom of the cabinet. This may cause light leaks but I have an answer for this as well.

If you're interested, I have several ideas of how to build light traps and air flow/multiple chamber options. Just let me know. Good luck with the project, interested in lots of pictures!

Duck

 

[iriebowl]

much thanks

much thanks

mahalo nui loa DiscoDuck (thankyou very much DiscoDuck)
I was hoping to get a reply like this where my problems are solved and better yet they get improved. I'm gonna go your way with the intake design. Its gonna be easier to do and save money on the PVC parts. With my original design, in the back of my head I was always thinking "isn't the hot exhaust air from the veg cab just gonna heat up the flower room even more instead of cool it?!?!". But your layout makes much more sense in efficient cooling overall. Now I have a question for you. Are you using any PVC elbows as light catches on your intakes? or are all your intake holes just holes? Also how are the temps in the cab?


heres my current grow that will be going into to cab when its built. the 3 bigger ones are about 4-5 weeks and the smaller ones are around 2 weeks.
(left to right)
front row hashberry, kalimist2, kalimist1
back row 2nd gen bagseed, bagseed, kalimist3
what you cant really see is my grapevine X lavender in the back corner.

 

[DiscoDuck]

mahalo nui loa DiscoDuck (thankyou very much DiscoDuck)
I was hoping to get a reply like this where my problems are solved and better yet they get improved. I'm gonna go your way with the intake design. Its gonna be easier to do and save money on the PVC parts. With my original design, in the back of my head I was always thinking "isn't the hot exhaust air from the veg cab just gonna heat up the flower room even more instead of cool it?!?!". But your layout makes much more sense in efficient cooling overall. Now I have a question for you. Are you using any PVC elbows as light catches on your intakes? or are all your intake holes just holes? Also how are the temps in the cab?


heres my current grow that will be going into to cab when its built. the 3 bigger ones are about 4-5 weeks and the smaller ones are around 2 weeks.
(left to right)
front row hashberry, kalimist2, kalimist1
back row 2nd gen bagseed, bagseed, kalimist3
what you cant really see is my grapevine X lavender in the back corner.

Hey iriebowl, nice plants. I was using scotchbrite in the intake holes to filter dust and diffuse the light that bled slightly out the back, against the floor molding. I'm getting tired of cleaning the dust out of the stuff every other week so I'm gonna try something new. This can be done inside the cabinet or underneath the floor of the cabinet, whichever works better.


This is a diagram of a cabinet footprint (top and side view) The broken diamond shaped things are 3/4 ~ 1" thick scrap wood used as a pedestal or spacer. The black dots represent intake holes drilled through the bottom of the cabinet. The broken rectangles are 1/2" plywood floor panels that are cut 1" smaller (length x width) than their respective chambers. The 1/2" panels are centered over the pedestal/spacer and glued/screwed to the pedestal.

I think this design is better than the cabinet I modified because my intakes are on the outer perimeter of the floor panel. Light leaks are and issue and have to be dealt with. With this version, the intakes are blocked by the 1/2" plywood panel while still allowing the air to pass through. If the dog side of the panel is painted black, this will help block light even better but might increase temps (probably no more than a degree.) If there's a down side to this idea I haven't figured it out yet. A circulation fan in each chamber would be a must because the air flows at the perimeter only. (Air will mix slightly in the chamber before exiting but a circulation fan is still necessary in my opinion.)

I just bought a few elbows the other day at the hardware store and they were only 50 cents a piece. You can probably get em cheaper at a plumbing supply. I designed my box with as little ducting as possibly because I was concerned about air flow restriction. After the fact, I realized I hadn't taken care of the light leak issues and had to go back to the drawing board.

My utility chamber sits atop my veg area and has the same intake configuration as the veg floor. This works excellent for air transfer but required scotchbrite to block light. I canned the sb and glued elbows (over the holes) to the ceiling of the veg room. Then I made one of those platform light traps and installed it on the floor of the utl. room. Most growers recommend fabricating 180 degree bends in your pvc to completely block any light from leaking. The reason I needed the platform trap is because I only used 90 degrees (one bend instead of two) and this alone would not have worked.

My next project is to make platform traps for the veg and flower rooms. I'll probably glue 90s underneath for redundancy. My inside temps average between four and eight degrees higher than ambient (about 6 degrees average.) Sugarbear says his temps are cool enough with a 150 so a cool tube isn't necessary. You'll probably do well with a computer fan blowing across the bulb without a tube. Have a good one.

 

[iriebowl]

wow thanks again for even more help and info. I will go with your new intake design for the points you stated. I bought all my materials and will be building this weekend. Only thing I need to buy again is some smaller hinges. The ones I bought are 2" long and 3/4" wide which makes it hard to use on 1/2" plywood. I saw some 30" hinges that were about 1/2" wide so Ill be getting those in return. For my intakes Ill be using regular door screen stapled to the entire base frame, then set my cab on that. Still gonna go with the cooltube since I got 2 150s in there and I already know temps will be the biggest issue, but Ill be sure to add some interior fans for extra movement.

cant wait to start assembling and post my cab for all to see. Hope i do some justice to your well planned designs.


stay irie

 

[DiscoDuck]

sounds like you're well on your way, look forward to the pics.